In the operation of a fluid system which serves work elements, such as for example the hydraulic system of an excavator which serves track, swing, stick, boom, and bucket work elements of the excavator, it is desirable to have a plurality of circuits and a plurality of work elements in each circuit. However, during operation of the excavator, it is often desirable to have additional fluid supplied to certain of the work elements under certain conditions. The problem then arises in being able to automatically supply this additional fluid under certain preselected conditions thereby avoiding placing additional requirements on the operator of manually manipulating additional controls to actuate the additional control elements.
The present invention is directed to overcome one or more of the problems as set forth above.
According to the present invention, a fluid system has first and second circuits each having a pump, a plurality of work elements connected in interruptible series, and a pilot pump connected to each work element through a respective control valve for controlling the operation of the work elements. A first fluid bypass line is connected at one end to the first circuit at a location between work elements of the first circuit and at the other end to the second circuit. A flow control valve is positioned in the first fluid bypass line. The flow control valve is movable between a first flow restricting position and a second open position. First means is provided for moving the flow control bypass valve to the second position in response to operation of selected work elements of the first circuit and for moving the valve to the first position in response to termination of operation of selected work elements of the first circuit. A second bypass line is connected at one end to the first circuit at a location between work elements of the first circuit and at the other end to the second circuit. Second means is provided for controllably passing fluid from the second circuit into the second bypass line in response to operation of preselected work elements of the first circuit.